OVERALL OBJECTIVES: To determine the physiologic relevance and importance of local regulatory factors in thyroid including: 1) prostaglandins; 2) thyroid hormones; 3) protein kinases and phosphoprotein phosphatase. GOALS SET FOR THE CURRENT YEAR: It is proposed to assess the relative contributions of TSH ("long-loop") and local regulatory factors ("short-loop" - e.g., thyroid hormones) to the overall regulation of thyroid function. 2. Studies of ornithine decarboxylase (ODC) activity in thyroid will focus on the relationship of this enzyme to cyclic AMP-dependent protein kinase activity. It is hoped that these studies will provide new insights into the role of the ODC enzyme in thyroid function. 3. Studies of phosphoprotein phosphatase and the response of this enzyme to TSH, LATS, prostaglandins and other thyroid stimulators. It is hoped that these studies will provide information as to whether activation of this enzyme provides a counter-regulatory mechanism to the activation of protein kinase in thyroid.